1. Field of the Invention
The present invention relates to an image sensor for use in an image inputting apparatus for reading an image such as a copier, a facsimile, etc.
2. Description of the Related Art
As an example of an image sensor for reading image information of a transmissive document or the like, FIG. 2 of JP-A-6-037972 (hereinafter referred to as “Patent Document 1”) discloses an image reading apparatus capable of reading a transmissive document. The image reading apparatus includes an upper moving unit that includes: a transparent plate for pressing the document; a transmitting light source for the transmissive document; and a reflecting plate 16 for a reflecting document.
Further, paragraph number 0038 of JP-A-2002-366942 (hereinafter referred to as “Patent Document 2) discloses an image reading system in which a peripheral edge portion of a document plate is provided with a white reference for a reflective document that has a uniform reflecting surface of high reflectance, and at a time of reading a film, light irradiated from a planer light source portion of a transmissive document unit is incident on a linear sensor through white reference windows of film holders.
However, although Patent Document 1 discloses the image reading apparatus for reading the transmissive document, Patent Reference 1 does not describe a specific configuration of enabling to read a stable high quality image even by a change in an environment of use or the like. Therefore, an image output is changed by TCR (temperature characteristic) provided to a mounted illuminating element (light emitting element) in accordance with a change in an environment of use or the like, which brings about unstable reading image quality. Further, a reading quality is deteriorated by a reduction in luminance in accordance with an aging change of an illuminating element caused by a long period of time of use.
Although Patent Document 2 discloses the image reading system that directly irradiates the document table through a white reference window installed at a folder of the film of the transmissive document unit 37 for determining whether the document is the transmissive document (film) or a reflective document, Patent Reference 2 does not teach an improvement of a reading quality of an image for the transmissive document.
Hence, it is an object of the invention to provide a novel image sensor capable of reducing a deterioration in the accuracy of reading the document.